The initial choice for WordPress was because of the content management system (CMS) and ease of use. WordPress also powers more than 31% of the web.
The key reasons to migrate from WordPress to a static site generator like Hugo are cost savings and speed. Other reasons include security, less complex customizations, and scalability/maintainability.
One of the main reasons for migration would be cost. With WordPress you will need a domain, and web hosting which includes a web server, PHP and a database. Most hosting plans will give you a good deal for the first year but after a couple years, it does get pricey.
Another reason to switch to a static site is page load speed. WordPress websites take longer to load because the pages are dynamically loaded. Whenever a user loads a WordPress website, it has to build the page from a template, grab the content and data from the database and then send the completed page to the user.
With a static site generator, you are hosting the static files with the content already inside of it. Whenever a user loads a static website, the content is already on the file so all the server needs to do is find the matching file and display it. The improves the page load speed significantly.
Below are tests I ran using Pingdom Website Speed Test on my WordPress and static site.
Static Site Test:
With static sites, there is no dynamic data storage which means there are less things a hacker can exploit. With WordPress, there are known exploits and with every WordPress plugin you install introduces a potential access point for hackers.
In conclusion, moving to a static site from a dynamic site like WordPress has many benefits including cost savings, quick page load times, and increased security.
Check out How to Choose the Best Static Site Generator for considerations when picking a static site generator and WordPress to Static Site Generator (Hugo) Migration and Deployment for steps on how to get started with the migration.